1. Field of the Invention
The present invention relates to a multi-channel assignment method in multi-hop wireless networks for the nodes with multiple wireless transceivers to utilize multiple non-orthogonal channels, and a more particularly to a dynamic multi-channel assignment method in multi-hop wireless networks, such as wireless mesh networks and wireless ad-hoc networks, for the relay nodes to improve the system throughput by concurrent transmission with multiple non-orthogonal channels.
2. Description of the Related Art
A Multi-hop wireless network has received interest, in the research of extending the reach of last-mile access to the Internet, using multi-hop configuration. The typical examples of multi-hop wireless networks are wireless mesh networks and wireless ad-hoc networks. This multi-hop wireless network consists of wireless relay nodes and subscribed nodes. A wireless relay node relays packets like a router in a fixed network through wireless channels. Some relay nodes are connected to the Internet and all subscribed nodes can access the Internet through multi-hop relaying. Considering that the main cost of wired networks is the deployment and maintenance of physical wires, multi-hop wireless networks are beneficial for swift deployment, low installation costs, and higher flexibility.
Typical examples of multi-hop wireless networks can be found in standardization activities. The WLAN (IEEE 802.11) and WIMAX (IEEE 802.16) technologies tackle wireless mesh networks. In IEEE 802.11, ESS (Extended Service Set) Mesh Networking (IEEE 802.11s) TG (Task Group) considers layer-2 mesh path selection and data forwarding for Mesh AP (Access Point)s. Mesh APs create a wireless backhaul network and provide Internet access service for the served nodes. Also, the WiMax standard and Multi-hop Relay (IEEE 802.16a/j) TG deal with multi-hop transmission to expand the coverage and improve the system throughput.
In this multi-hop wireless network, non-overlapping channels can be used to improve the system performance via simultaneous transmission within a neighborhood. For example, 3and 12 non-overlapping channels are available in the IEEE 802.11b/g and 802.11a standard, respectively. Also, multiple radio interfaces are feasible in a single relay node since the prices of RF transceivers have gone down. For example, some products equipped with multiple radios have been commercially merchandized.
In this multi-radio multi-channel wireless network, the channel allocation method affects system performance. Multiple channels should be allocated to minimize interference among channels. Channel interference in multi-hop configuration has three factors. First, each node experiences different channel interference. Due to the fading effect of wireless channels, each node has different channel quality, according to its location and environment. Therefore, each node can prefer different channels by its noise level. Second, neighboring paths that use the same channel interfere with each other. When two paths use the same channel within an interference range, two flows cannot be transmitted simultaneously. This interference is the inter-flow interference. Third, there exists interference among adjacent hops on the same path. If consecutive links of path within the interfering range are allocated with the same channel, packets that belong to a flow cannot be transmitted simultaneously on consecutive links. This is the intra-flow interference. To maximize network throughput, the above channel interference should be considered in a multi-channel assignment problem.